With the growing interest in rapid prototyping and manufacturing, commonly known as additive manufacturing or 3-D printing, a number of techniques have been developed for the production of dense spherical powders, which are useful for such technologies. The success of additive manufacturing and 3-D printing depends in a large extent on the availability of materials usable for parts manufacturing. Such materials need to be provided in the form of highly pure, fine (e.g. diameter less than 150 μm), dense, spherical, and free-flowing powders that have well-defined particle size distributions. Conventional melt atomization techniques such as gas, liquid and rotating disc atomization are unable to produce such high quality powders.
More recent techniques avoid the use of crucible melting, which is often responsible for material contamination. These recent techniques provide spherical, free-flowing powders.
For example, some plasma atomization processes are based on the use of a plurality of plasma torches producing plasma jets that converge toward an apex. By feeding a material to be atomized in the form of a wire or rod into the apex, the material is melted and atomized by thermal and kinetic energy provided by the plasma jets. It has also been proposed to feed a material to be atomized in the form of a continuous molten stream directed towards an apex where several plasma jets converge. These types of plasma atomization processes are rather delicate and require laborious alignment of at least three plasma torches in order to have at least three plasma jets converging toward the apex. Due to the physical size of such plasma torches, the apex location is bound to be a few centimeters away from an exit point of the plasma jets. This causes a loss of valuable thermal and kinetic energy of the plasma jets before they reach the apex position and impinge on the material. Overall, these processes involve several difficulties in terms of requirements for precise alignment and power adjustment of the torches and for precise setting of the material feed rate.
Other technologies are based on the use of direct induction heating and melting of a wire or rod of a material to be atomized while avoiding contact between the melted material and a crucible. Melt droplets from the rod fall into a gas atomization nozzle system and are atomized using a high flow rate of an appropriate inert gas. A main advantage of these technologies lies in avoiding possible contamination of the material to be atomized by eliminating any possible contact thereof with a ceramic crucible. These technologies are however limited to the atomization of pure metals or alloys. Also, these technologies are complex and require fine adjustment of operating conditions for optimal performance. Furthermore, large amounts of inert atomizing gases are consumed.
Therefore, there is a need for techniques for efficient and economical production of powder particles from a broad range of feed materials.